First, I would like to say that I don't expect anyone to take my conclusions as gospel. I'd worry about you if you did. But far too many people make decisions, their own conclusions, with no basis in any real testing. I personally feel that thousands of people are out there poling their brains out every weekend and don't really know for sure that it's doing any good. Perceived exertion may be important, but real world testing is better. I also think there are thousands of people out there totally dismissing trekking poles without every giving them a real shot.
Here are my conclusions about trekking poles:
They save your knees and hips when stepping up or stepping down from big rocks on the trail.
They are a huge help in crossing streams.
They can aid balance.
I think they are a performance help on steep to really steep grades.
I don't think that they will help you reach that alpine lake any faster, or less tired.
There are two types of poles:
Well, more than that, but the two basic kinds are the T-grip or cane type poles, and the standard vertical grip.
My conclusion is that the T-grip is vastly better for down hills, and the vertical grip is better for up hills. Although some cane grip poles have a vertical grip under the T-grip, they are a little short to use this way, at least for me, and you can't use the strap in the way you can on vertical grip poles (see instructions on using cross country poles).
The ideal pole doesn't exist. That would be a longer cane grip pole with a regular vertical grip and strap underneath.
Adjustable or non adjustable:
Adjustable can be really convenient, especially if you haven't established the ideal length for you. Plus you can change length for different terrain. There are two types of clamps: the twist kind and the clamp kind. I'm inclined to think the clamp kind are more secure.
On the other hand, it is really annoying, even dangerous, when the poles suddenly shrink in size while you are putting weight on them. I hate that.
Right now, I'm inclined to go with either a folding or one piece.
Well, lighter is better, but stronger is better too. I'd be warry of poles that are both cheap and light. Want a good, light pole? It's going to cost you.
Carbide is king. I think Lekki has really good points. Kompedell not so good, Mountain Smith are in between. Can't vouch for any others, but Black Diamond look like great poles all around.